Re: [tcpdump-workers] Problems with libpcap and C++
Ury Segal wrote: The buttom of the problem is this: You excpect libpcap to call X::dumper in the context of an instance of class X. (The "real" first parameter of "X::dumper" is a variable named "this" of the type "X*".) But the libpcap API is not defining a `void (X::)(u_char*, const pcap_pkthdr*, const u_char*)' Therefore, you cannot pass a non-static member function to libpcap. You can make dumper() a static member. Yes. If I make dumper() a static member of class X, then the compiler accepts it. It works even if I use it whithin a concrete instance of X. I mean the following two ways are accepted: X x; pcap_loop(..., x.dumper, ...); pcap_loop(..., X::dumper, ...); Thanks. __david - This is the tcpdump-workers list. Visit https://lists.sandelman.ca/ to unsubscribe.
Re: [tcpdump-workers] Problems with libpcap and C++
On Wed, Jun 14, 2006 at 04:48:02PM +0200, David Rosal wrote:
> I'm writing a packet sniffer in C++ using libpcap-0.9.4.
>
> I've tried to use a class function member as a callback for
> pcap_loop(), but the compiler complains that arguments don't
> match. The code is something like this (I have simplified it):
>
> 8<-
>
> class X
> {
> public:
> // This is the callback, defined below
> void dumper(u_char *u, const struct pcap_pkthdr *h,
> const u_char *p);
> };
To pass a C++ member function as a callback it must be static, or you
must have mechanisms to allow you to pass an instantiated object as
well.
-m
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Re: [tcpdump-workers] Problems with libpcap and C++
The buttom of the problem is this:
You excpect libpcap to call X::dumper in
the context of an instance of class X.
(The "real" first parameter of "X::dumper"
is a variable named "this" of the type "X*".)
But the libpcap API is not defining a
>`void (X::)(u_char*, const pcap_pkthdr*, const
> u_char*)'
Just a
> void (*)(u_char*, const pcap_pkthdr*, const
> u_char*)
Which is what the compiler is telling you.
Therefore, you cannot pass a non-static member
function to libpcap. You can make dumper() a
static member.
--- David Rosal <[EMAIL PROTECTED]> wrote:
> Hello.
>
> I'm writing a packet sniffer in C++ using
> libpcap-0.9.4.
>
> I've tried to use a class function member as a
> callback for
> pcap_loop(), but the compiler complains that
> arguments don't
> match. The code is something like this (I have
> simplified it):
>
> 8<-
>
> class X
> {
> public:
> // This is the callback, defined below
> void dumper(u_char *u, const struct
> pcap_pkthdr *h,
> const u_char *p);
> };
>
>
> void X::dumper(u_char *u, const struct
> pcap_pkthdr *h, const
> u_char *p)
> {
> // stuff...
> pcap_dump(blah, blah, blah);
> }
>
>
> int main()
> {
> X x;
>
> // Open pcap, etc...
>
> pcap_loop(p, -1, x.dumper, 0);
> }
>
> ->8
>
> And g++ says this:
>
> In function `int main()':
> sniffer.cc:645: error: argument of type `void
> (X::)(u_char*,
> const pcap_pkthdr*, const u_char*)' does not
> match `void
> (*)(u_char*, const pcap_pkthdr*, const
> u_char*)'
>
> This is not a warning but an error, so I cannot
> compile the program.
>
> Is there any trick to fix this? Am I missing
> something?
>
> Should I avoid C++ and use C instead (don't say
> that please...)
>
>
> Thanks.
>
>
> __david
> -
> This is the tcpdump-workers list.
> Visit https://lists.sandelman.ca/ to
> unsubscribe.
>
--ury
-
This is the tcpdump-workers list.
Visit https://lists.sandelman.ca/ to unsubscribe.
Re: [tcpdump-workers] Problems with libpcap and C++
David Rosal wrote: I've tried to use a class function member as a callback for pcap_loop(), but the compiler complains that arguments don't match. The code is something like this (I have simplified it): ... Should I avoid C++ and use C instead (don't say that please...) Should you avoid C++ completely? No. Should you avoid writing the callback routine passed to pcap_loop() in C++? No, but you should avoid, as far as I know, making it a class method, because it's not going to be passed a "self" pointer. I'd suggest writing your own capture loop and using pcap_next_ex() instead, if you want to have the packet processing done by a class member. - This is the tcpdump-workers list. Visit https://lists.sandelman.ca/ to unsubscribe.
